[Mondrian] hanging application: segment cache manager and schema load?

[Wright, Jeff]

We've seen our application hang a couple times. Looking at thread dumps, I'm suspicious of this excerpt:

"mondrian.rolap.agg.SegmentCacheManager$ACTOR" daemon prio=10 tid=0x00007f1b34170000 nid=0xf25 waiting for monitor entry [0x00007f1ad965f000]
   java.lang.Thread.State: BLOCKED (on object monitor)
                at mondrian.rolap.RolapSchemaPool.getRolapSchemas(RolapSchemaPool.java:420)
                - waiting to lock <0x00000005e23c2028> (a mondrian.rolap.RolapSchemaPool)
                at mondrian.rolap.RolapSchema.getRolapSchemas(RolapSchema.java:930)
                at mondrian.rolap.agg.SegmentCacheManager.getStar(SegmentCacheManager.java:1621)
                at mondrian.rolap.agg.SegmentCacheManager$Handler.visit(SegmentCacheManager.java:661)
                at mondrian.rolap.agg.SegmentCacheManager$ExternalSegmentCreatedEvent.acceptWithoutResponse(SegmentCacheManager.java:1222)
                at mondrian.rolap.agg.SegmentCacheManager$Actor.run(SegmentCacheManager.java:1019)
                at java.lang.Thread.run(Thread.java:724)

I don't fully understand SegmentCacheManager, but based on Julian's 2012 blog post I get the impression the Actor thread is supposed to run very. If that corresponds to the stack trace above, that's a big problem - we see schema loads take minutes.

I also see that there were some code changes in August last year for MONDRIAN-2390, to make locking for schema load lower level. We don't have that code.

Btw we have a distributed cache.

Does it sound like I'm on to a problem in our environment? Maybe even a general problem?

--Jeff Wright
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